Extreme weather events, from droughts to floods and heat waves, are some of the most tangible present day impacts of global warming, and they will take center stage in speeches at the upcoming Paris Climate Summit. Now a new report gives leaders pushing to reduce emissions of global warming pollution, including President Obama, additional ammunition.

The report, published Thursday as a special supplement to the Bulletin of the American Meteorological Society, amounts to the largest-ever assessment of global warming’s role in intensifying the severity and altering the likelihood of extreme weather events during 2014.

It amounts to the equivalent of a climate change CSI report, and its conclusions are damning in pointing to global warming as being an accomplice to numerous damaging extreme events worldwide.

A firefighter puts down hot spots in front of a house in the hills May 14, 2014 in San Marcos, California.

Image: Bill Wechter

In total, the report contains analyses from 32 different research groups examining 28 extreme weather and climate events on all continents. The dozens of researchers from 21 countries found that climate change’s fingerprints are all over the scene of the crime in more than half of these events, including California wildfires, Middle Eastern drought and heat waves in Australia.

Specifically, tropical cyclones in the central Pacific, deadly heat waves in Australia, Asia and South America, and a deadly snowstorm in the Himalayas, were each in part the result of human activities, the studies show.

“For each of the past four years, this report has demonstrated that individual events, like temperature extremes, have often been shown to be linked to additional atmospheric greenhouse gases caused by human activities, while other extremes, such as those that are precipitation related, are less likely to be convincingly linked to human activities,” said Tom Karl, director of the National Centers for Environmental Information in Asheville, North Carolina.

“As the science of event attribution continues to advance, so too will our ability to detect and distinguish the effects of long-term climate change and natural variability on individual extreme events. Until this is fully realized, communities would be well-served to look beyond the range of past extreme events to guide future resiliency efforts."

These studies are part of a new and increasingly sophisticated subfield within climate science known as extreme event attribution, which involves attempts to tease out the influence of climate change, natural variability and other factors that go into extreme events.

A photo, sent by members of the Alpine Club on 20 October, 2014, shows the ascent from Tilicho Lake (Tea House) to the Tilicho base camp near the Annapurna Massif in heavy snowfall in Nepal, 16 October 2014.

Image: dpa/Corbis

Notably, each of the assessments of extreme climate events in Australia found clear evidence of human influences, including increased likelihood of a heat wave in Brisbane, Australia, heat waves in Adelaide and Melbourne in January 2014, record warm spring temperatures across Australia.

Manmade extremes

The events that had a manmade component to them included tropical cyclones that hit Hawaii, the Argentinean heat wave of 2013, and Australian heat waves.

Four separate studies by different scientific teams found that human influences, mainly in the form of increased emissions of global warming pollutants, caused a substantial increase in the likelihood and severity of several heat waves that struck Australia in 2014. These included events in Melbourne and in Brisbane, where extreme heat hit during the G20 Summit and global warming was conspicuously absent from leaders’ agenda.

For example, climate model simulations for 2014 indicated that manmade global warming “very likely increased the likelihood of hot and very hot November days in Brisbane by at least 25% and 44% respectively,” the G20 heat wave study concluded.

Another study published Thursday found that the record warm Australian spring of 2014, during which all-time temperature records were exceeded across the continent, “would likely not have occurred without increases in carbon dioxide over the last 50 years,” combined with weather patterns in the upper atmosphere.

A man who collapsed due to heat is helped by paramedics into an ambulance during a protest for aboriginal rights on November 14, 2014 in Brisbane, Australia.

Image: Daniel Munoz/Getty Images

Perhaps the most fascinating, albeit extremely deadly, event scientists analyzed was the blizzard that killed 43 people, including 21 trekkers, in the Himalayas. This storm resulted from the combination of Category 4 Tropical Cyclone Hudhud with other weather systems in a rare confluence of extreme events.

The study found that climate change increases the odds of such “unusual mergers” between tropical cyclones and upper level weather disturbances, because of the ways it is changing weather patterns in that region. The study detected a northward shift in intense tropical cyclones in the Bay of Bengal, as well as an intensification in the strongest storms that have occurred as water temperatures in the area have increased.

These changes have raised the risk of such storms in northeastern India and increased the frequency of extremely high amounts of moisture slamming up against the wall of the Himalayan Mountains in Nepal, where such water vapor falls as heavy snow.

“The implication of these results is that, although weather systems similar to that of 13–14 October 2014 did occur in the past, there is a tendency for both types of weather systems to interact more frequently,” the study said.

The Nepal disaster, which was the deadliest event in the history of Nepal’s mountain climbing history, had some similarities to Hurricane Sandy, when a massive tropical cyclone in the Western Atlantic interacted with a feature in the jet stream to bring several feet of snow to West Virginia while flooding parts of the East Coast with a deadly storm surge.

In addition, another study using computer modeling found that manmade global warming has increased the odds of unusually high sea surface temperatures in the western tropical Pacific Ocean and northeast Pacific Ocean. Such temperature extremes contributed to record heat in Alaska and whole scale shifts in the distribution of sea life, as well as changes in tropical cyclone behavior in the western tropical Pacific.

Many studies turned up little evidence of a manmade influence

Many studies did not turn up a manmade influence on particular extreme events, although every weather event today takes place in an atmosphere altered by manmade activities.

One study by scientists at Spain’s Barcelona Supercomputing Center, found that the all-time maximum in Antarctic sea ice in 2014 was mainly the result of unusual wind patterns that enhanced offshore production of sea ice. The study found that these winds, and the resulting spike in sea ice extent, are now less likely to occur due to climate change.

Local men look on at Bronte Beach on May 23, 2014 in Sydney, Australia. Sydney is experiencing its hottest May on record, already recording its hottest week for this time of year in over 150 years.

Image: Ryan Pierse/Getty Images

All-time maximum of Antarctic sea ice in 2014 resulted chiefly from anomalous winds that transported cold air masses away from the Antarctic continent, enhancing thermodynamic sea ice production far offshore. This type of event is becoming less likely because of climate change.

The authors of the overall report noted that attribution assessments are limited by the often limited observational records and limitations of computer models. “In general, when attribution assessments fail to find anthropogenic [manmade] signals this alone does not prove anthropogenic climate change did not influence the event,” the report states. “The failure to find a human fingerprint could be due to insufficient data or poor models and not the absence of anthropogenic effects.”

Looking back a year later: what’s the relevance to society?

The examination of 2014’s extremes demonstrates a major weakness of these studies so far, which is that they frequently take so long to be completed that they come months or a year or more after the events themselves. This is well after such events have disappeared from the news, and after many of the governmental leaders who dealt with these events — such as former Australian Prime Minister Tony Abbott — have left office.

Such studies often require supercomputing resources obtained either through national supercomputing centers — such as at Barcelona or the National Center for Atmospheric Research in Colorado — or distributed computing, in which everyday citizens use their home computers’ down time to perform computations for climate scientists. This project, known as Weather At Home, is led by a team in the U.K. and partially funded by The Guardian newspaper and Microsoft.

“Understanding our influence on specific extreme weather events is groundbreaking science that will help us adapt to climate change,” said Stephanie Herring, lead editor for the report.

“As the field of climate attribution science grows, resource managers, the insurance industry, and many others can use the information more effectively for improved decision making and to help communities better prepare for future extreme events.”

There are ongoing efforts to change this, however, and make more rapid assessments.

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